Direct wafer bonded InP-GaAs structures are studied by FTIR infrared absorbance spectra and FESEM cross-sectional observations. Experiments show that the non-uniformity of bonding pressure during the fabricating step results in the appearance of a spacer-layer at the InP-GaAs interface. By melting wax and filling it into this spacer-layer, locally unbonded areas can be characterized upon the opt ical absorbance peaks at 3.509 μm. The 3.509 μm absorbance-intensity mapping images the non-uniform distribution of bonding pressure, which was obtained by t wo-dimensionally scanning measurement of infrared spectra of samples. Uniformly bonded InP-GaAs structures with uninterrupted interface are fabricated after imp roving the uniformity of pressure of fixture, which will be prospect of preparin g for large scale wafer bonding structures such as optical micro-cavity structur es.